Single use syringe

ABSTRACT

A syringe (10) comprises a barrel (12), a plunger (14) and a retractable needle mount (16). The needle mount (16) is secured in an opening in one end (20) of the barrel by resiliently flexible arms (64) having shoulders (62) which cooperate with shoulders (32) defined in recesses (28) of the barrel wall (36) by insert ring (24) seated on step (22). The plunger piston (96) has slots (114) in an end face thereof which closely receive the distal portions (74) of the arms (64) widthwise. The slots (114) have surfaces (116) which act on the arms to disengage the arms from the recesses (28) and catches (122) which cooperate with catch surfaces (80) on the arms so that the needle mount (16) is withdrawn with the plunger (14). The barrel (12) includes integrally hinged guide members (126) to axially orientate the plunger (14) relative thereto and the plunger has catch means (140) which cooperates with the guide member (126) to secure the withdrawn plunger.

TECHNICAL FIELD

This invention relates in one aspect to a syringe having a retractableneedle mount and in another aspect to a syringe providing improvedefficiency of assembly.

BACKGROUND ART

Preventing accidental injury and infection from used hypodermic needleshas attracted considerable interest in recent years. One way of reducinginjury and infection is by retracting a needle into the syringe barrelafter use. There has been a very large number of different arrangementsproposed for achieving this, but it has become clear that none of theseproposals is likely to become commercially acceptable unless the needlemount engaging and retraction is entirely automatic so that noadditional steps have to be performed by the operator, the needle mountis securely located in the end of the syringe barrel during use, thesyringe is relatively cheap and simple to manufacture yet reliable, andthe volume of the dead space between the engaged plunger and needlemount is negligible.

One arrangement which has shown hope of meeting some of theserequirements includes a needle mount having a deformable securingportion to disengageably retain the needle mount within one end of thebarrel, means on the plunger to deform the securing portion as theplunger approaches the needle mount to disengage the engagement of theneedle mount with the barrel and cooperable means on the plunger and onthe needle mount to enable the plunger to engage the disengaged needlemount for withdrawal of the needle mount into the barrel when theplunger engaged with the needle mount is displaced away from the one endof the barrel.

One such proposal is illustrated in FIG. 6 of European PatentApplication EP-A360313. Another such proposal is illustrated in FIGS. 7and 8 of European Patent Application EP-A-321903, and yet another sucharrangement is described in the Applicant's International PatentApplication WO91/07198 (the contents of which and of correspondingpatents and patent applications including U.S. Pat. No. 5,378,240 areincorporated herein by reference).

In arrangements such as these, it has been found that the deformablesecuring portion on the needle mount should comprise at least oneresiliently flexible arm of relatively small cross section in order toensure its ready disengagement from the barrel with minimal resistanceto movement of the plunger, that is so that the disengagement occursautomatically with essentially no additional input from the operator. Aproblem with this is that the arm may not be very strong and may tend tobe subjected to undesirable deformation resulting in disengagement fromthe plunger if there is any substantial resistance to withdrawal of theneedle mount into the barrel with the plunger.

In EP-A-360313, the syringe barrel is described as having elastic clawswhich grip a needle mount located in the opening in the barrel. Thisgrip is not released when the plunger engages the needle mount and islikely to present undesirable resistance to withdrawal of the needlemount into the barrel. Likewise, as clearly seen in FIG. 8 ofEP-A-321903, there are several restrictions to withdrawal of the needlemount into the barrel with the plunger.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided asyringe comprising a barrel having an opening therethrough at one end, aplunger operable axially within the barrel and a needle mount in theopening which is prevented from displacement outwardly through theopening and has a securing portion comprising a resiliently flexible armextending generally away from said one end towards the plunger, said armhaving a shoulder on a radially outwards surface thereof whichcooperates with a shoulder on the barrel wall to resist withdrawal ofthe needle mount from the opening into the barrel, the syringe furthercomprising a surface portion on the plunger to deform the arm radiallyinwardly as the plunger approaches the needle mount thereby to disengagethe arm from the barrel wall shoulder, and cooperable engagementsurfaces on the plunger and on a distal end of the arm whereby theplunger is capable of engaging the disengaged needle mount forwithdrawal of the needle mount into the barrel when the plunger isdisplaced away from said one end of the barrel, wherein means isprovided to resist sideways deformation of the arm when the arm isengaged by the plunger for withdrawal of the needle into the barrel.

The means to resist sideways deformation of the arm advantageouslycomprises slot means in which the arm is radially displaceable, the slotmeans having such a width as to closely receive the arm. The slot meansmay comprise a slot provided in the needle mount and the arm may bereceived within the slot along substantially its entire length. Morepreferably, however, the arm projects into the barrel relative to atleast adjacent portions of the needle mount and the slot means comprisesa slot in an end face of the plunger, in which the engagement surface onthe plunger is conveniently provided, which receives the distal end ofthe arm.

In addition to resisting deformation of the arm, closely receiving thearm within the slot means has the major advantage of helping to reducedead space between the needle mount and the plunger when the plunger andneedle mount are engaged. This is important since the volume of the deadspace quantifies the volume of residual liquid injectate in the syringeat the end of the plunger injecting stroke. Australian HealthRegulations limit the dead space in a syringe, for example to a maximumof 0.075 ml for a 5 ml syringe.

To further reduce the dead space between the engaged plunger and needlemount, an end face of the plunger advantageously has a substantial partof its surface area in at least very close overlying relationship with acorresponding end face of the needle mount when the plunger and needlemount are engaged. By "substantial" is meant at least 50%, preferably atleast 75% and more preferably at least 85% of the surface area. Theneedle mount will have an injectate flow passage therethrough fordirecting the injectate to a cannula or needle in use, and preferablythe flow passage is not sealed by the plunger when it cooperably engagesthe needle mount. This helps to ensure that as much of the injectate aspossible is able to pass into the flow passage.

The needle mount securing portion may comprise more than one resilientlyflexible arm, and the syringe advantageously has a needle mount securingportion comprising a second resiliently flexible arm extending generallyaway from said one end towards the plunger, said second arm having ashoulder on a radially outwards surface thereof which cooperates with arespective shoulder on the barrel wall to resist withdrawal of theneedle mount from the opening into the barrel, with a second surfaceportion being provided on the plunger to deform the second arm radiallyinwardly as the plunger approaches the needle mount to disengage thesecond arm from the associated barrel wall shoulder.

If it is desired to cant the needle mount over as it is withdrawn withthe plunger, the aforementioned second arm need not be engaged by theplunger to facilitate withdrawal of the needle mount into the barrel,but preferably cooperable engagement surfaces are provided on theplunger and on the distal end of the second arm whereby the plunger iscapable of engaging the disengaged needle mount thereby to facilitatewithdrawal of the needle mount into the barrel when the plunger isdisplaced away from said one end of the barrel, and means is provided toresist sideways deformation of the second arm when the arm is engaged bythe plunger for withdrawal of the needle into the barrel.

The means to resist sideways deformation of the second armadvantageously comprises associated slot means in which the second armis radially displaceable, the slot means having such a width as toclosely receive the second arm. The slot means may comprise a slotprovided in the needle mount and the second arm may be received withinthe slot along substantially its entire length. More preferably,however, the second arm projects into the barrel relative to at leastadjacent portions of the needle mount and the associated slot meanscomprises a respective slot in the end face of the plunger, in which theassociated engagement surface on the plunger is conveniently provided,which receives the distal end of the second arm.

The two means to resist sideways deformation, respectively of thefirst-mentioned arm and of the second arm, preferably take the sameform.

Most advantageously, in the preferred embodiment in which the distal endof the or each arm is received in a respective slot in the plunger, theor each deforming surface portion on the plunger is provided in therespective slot. Preferably the or each deforming surface portionengages a ramp surface on the respective arm.

The or each resiliently flexible arm of the needle mount is preferablypivoted from the side of the needle mount at a location remote from theaxially inner end of the needle mount, and most preferably the or eachsaid arm is deformable radially inwardly in a respective slot in theside wall of the needle mount which has such a width as to closelyreceive the portion of the associated arm therein. Thus, in thepreferred embodiment in which the distal end of the or each arm isclosely received in a respective slot in the plunger end face to provideresistance against sideways deformation of the arm, the arm isadditionally supported against sideways deformation by the associatedslot in the needle mount. This has the advantage of not only helping toresist sideways deformation of the arm, but also to reduce the deadspace between the engaged plunger and needle mount while readilyallowing for the desired degree of resilient flexibility of the or eacharm. The or each resiliently flexible arm is advantageously pivotedabout an integral joint which provides at least the majority of theresilient flexibility of the arm.

The resilient flexibility of the or each arm advantageously biases thearm to normally maintain the cooperation between the respectiveshoulders on the arm and on the barrel wall and, during withdrawal ofthe needle mount, between the cooperable surfaces on the plunger and onthe distal end of the arm.

Advantageously, the shoulder on the or each resiliently flexible arm ofthe needle mount is closely received in an associated recess includingthe barrel wall shoulder which substantially conforms to a portion ofthe arm on which the arm shoulder is formed. Again this helps to reducethe dead space between the engaged plunger and needle mount. It alsomeans that the needle mount must be carefully axially oriented to ensurethat the or each needle arm shoulder is received in the associatedrecess in the barrel wall, and advantageously cooperating locating meansare provided on the needle mount and barrel wall. If at least one of theneedle mount arms is closely received in an associated slot in theplunger end face when the plunger and needle mount are engaged, it isthen also advantageous to ensure that the plunger is correctly orientedaxially, and preferably axial guide means for the plunger arecoordinated with the aforementioned needle mount locating means.

According to a second aspect of the present invention, there is provideda syringe comprising a moulded barrel, a needle mount at one end of thebarrel, a plunger having a piston which is axially displaceable withinthe barrel by means of a plunger shaft which projects from an opening atthe other end of the barrel, the plunger shaft having a non-circularcross-section, and guide means for rotationally orienting the plungerrelative to the barrel the guide means being integrally moulded with thebarrel and connected thereto by integral hinge means whereby in an opencondition of the guide means the plunger piston may be introduced to thebarrel through said opening and in the closed condition the guide meansoverlies the other end of the barrel and partly closes said opening tocooperate with said non-circular cross-section of the plunger shaft toprovide said rotational orientation, the needle mount being retractableinto the syringe barrel from said one end after an injecting stroke andhaving a deformable securing portion to disengageably retain the needlemount within the one end of the barrel, means on the plunger to deformthe securing portion as the plunger approaches the needle mount todisengage the engagement of the needle mount with the barrel andcooperable means on the plunger and on the needle mount to enable theplunger to engage the disengaged needle mount for withdrawal of theneedle mount into the barrel when the plunger engaged with the needlemount is displaced away from the one end of the barrel, and whereincooperating locating means are provided on the barrel and on the needlemount to rotationally orientate the needle mount relative to the barrelwhereby the needle mount is rotationally oriented relative to theplunger.

The integral hinging of the guide means reduces the number of componentsof the syringe to be assembled and assists the proper orientation of theguide means over the opening at the other end of the barrel. and therebycan ensure the correct rotational orientation of the plunger. The guidemeans advantageously comprises locating means which cooperates withcorresponding means on an end face of the barrel at the other end, forexample a peg on one and a corresponding aperture on the other, when theguide means is in its closed condition to ensure the proper orientationof the guide means over the opening. By partly closing the opening, theguide means prevents full withdrawal of the plunger from the barrel. Theguide means may conveniently be secured in the closed condition, forexample, by welding or otherwise bonding.

The guide means advantageously comprises opposed guide members each ofwhich is integrally hinged to the barrel at the other end, on oppositesides of the opening. When the guide members are folded into the closedcondition they preferably together define an aperture therethrough whichsubstantially corresponds in cross-section to that of the plunger shaft.For example if the cross-section of the plunger shaft is a cross, thatof the aperture may also be a cross, albeit slightly larger to ensurefree sliding movement of the plunger shaft through the aperture.

The syringe according to the second aspect of the invention includes aneedle mount which is retractable into the syringe barrel from said oneend after an injecting stroke to reduce the risk of re-use of thesyringe and of needle-stick injuries.

It may be important that the needle mount is correctly rotationallyorientated relative to the plunger to provide the cooperation with thedeforming means and between the cooperable means, and the cooperatinglocating means are provided on the barrel and on the needle mount toensure the correct rotational orientation of the needle mount.

In a preferred embodiment the syringe according to the second aspect ofthe invention is also in accordance with the first aspect of theinvention.

Advantageously in both the first and the second aspect of the invention,cooperating means are provided on the plunger and on the barrel toprevent forward movement of the plunger once the plunger has beenwithdrawn into the barrel after an injecting stroke. The cooperatingmeans conveniently comprises a catch on the plunger which cooperateswith the aforementioned guide means in a syringe in accordance with thesecond aspect of the invention. Preferably the plunger has a line ofweakness adjacent the piston which is exposed when the plunger has beenwithdrawn after an injecting stroke so that the plunger shaft can bereadily snapped off by the operator.

As noted already, a disadvantage of previously proposed syringes withretractable needle mounts is the cost of manufacture. Moulding costs areincreased in any product when the product includes an undercut portionwhich has to be formed by one or more removable inserts. In a syringecomprising a moulded barrel having an opening therethrough at one end, aplunger operable within the barrel and a needle mount in the opening,the needle mount having a deformable securing portion which engages ashoulder on the barrel wall to resist withdrawal of the needle mountinto the barrel from the one end thereof, means on the plunger to deformthe securing portion as the plunger approaches the needle mount todisengage the engagement of the needle mount with the barrel shoulderand cooperable means on the plunger and on the needle mount to enablethe plunger to engage the disengaged needle mount for withdrawal of theneedle mount into the barrel when the plunger engaged with the needlemount is displaced away from the one end of the barrel, such as asyringe in accordance with the first aspect of the invention, theshoulder on the barrel wall may form an undercut portion if the one endof the barrel has smaller cross-section than the remainder of thebarrel.

Such an undercut portion formed by the barrel wall portion can beavoided if the barrel wall shoulder is moulded into the barrel wall andthe needle mount is disposed in an insert which is introduced into saidone end of the barrel and sealed in place so as to prevent withdrawal ofthe needle mount outwardly through the opening. In this embodiment, theshoulder on the or each arm of the needle mount in a syringe accordingto the first aspect of the invention is engaged with the associatedbarrel wall shoulder from said one end of the barrel.

Such an undercut portion formed by the barrel wall portion canalternatively be avoided in accordance with a third aspect of theinvention when the shoulder is defined by an insert, such as a ring,secured to the barrel.

The insert is secured in place after initial moulding of the barrel, forexample by welding or otherwise bonding. The insert is preferablylocated by a step in the barrel wall. The step may extend fully aroundthe barrel wall and may have a radial width no greater than the insertexcept where the shoulder is defined in which case the shoulder isdefined in a recess in the step. Advantageously at least two recesses,preferably two opposed recesses, are provided in the step to define atleast two shoulders. While this feature of a recess(es) is applicable toother syringes, it is particularly advantageous in a syringe inaccordance with the first aspect of the present invention in which theaxial orientation of the needle mount is important, as previouslydescribed.

The needle mount in the syringe in accordance with the third aspect ofthe invention is introduced to the barrel from an opposite end of thebarrel.

While the three aspects of the present invention may be adopted indifferent syringes, any two of the aspects may advantageously be used inone syringe and in the preferred embodiment the syringe incorporates allthree aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of a syringe in accordance with the three aspects of thepresent invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a sectional view along the axis of one end only of a 5 mlsyringe showing a needle mount secured in an opening in a barrel and aplunger approaching the needle mount;

FIG. 2 is a view corresponding to FIG. 1 but showing the needle mountreleased from the barrel and engaged with the plunger so as to be freelywithdrawable into the barrel with the plunger;

FIG. 3 is a sectional view along the axis of the needle mount takennormal to the section of FIG. 1;

FIG. 4 is a plan view of the axially inner end of the needle mount;

FIG. 5 is a plan view of the axially outer end of the needle mount;

FIGS. 6 and 7 are elevational views of the needle mount taken normal toeach other;

FIGS. 8 and 9 are elevational views taken normal to each other of theplunger of FIG. 1 at a smaller scale;

FIG. 10 is a plan view of the axially inner end of the plunger at thescale of FIGS. 1 to 7;

FIG. 11 is a cross-sectional view of the plunger taken on the line A--Aof FIG. 9 but at the scale of FIG. 10;

FIGS. 12 and 13 are sectional views taken normal to each other along theaxis of the barrel of FIG. 1 at the smaller scale of FIGS. 8 and 9;

FIGS. 14 and 15 are plan views of the barrel from the other endrespectively showing end members thereof in the open and closedconditions at the smelter scale of FIGS. 12 and 13; and

FIG. 16 is a part sectional elevational view of the other end of thesyringe at the scale of FIGS. 1 to 7, showing the needle mount retractedwith the plunger, the plunger prevented from further forwards movementand the plunger handle snapped off.

DETAILED DESCRIPTION OF THE DRAWINGS

The syringe 10 comprises a barrel 12, a plunger 14 and a needle mount16.

The barrel 12 is open at both ends, but is inwardly stepped at one end20 at which the needle mount 16 is located. The barrel, plunger andneedle mount are all formed of a medical grade polypropylene, so thatthe syringe 10 is suitable for gamma ray sterilisation. The plunger 14carries a sealing ring 18 formed of a medical grade synthetic rubbersuch as Santoprene made by Monsanto.

Referring to FIGS. 1, 2, 12 and 13, the inner surface of the one end 20of the barrel 12 has a first annular step 22 onto which a locking ring24 (FIGS. 1 and 2) is ultrasonically welded, and a second annular step26 on which the needle mount 16 is seated. Small opposed recesses 28 arealso formed in the inner surface of the one end 20 of the barrel betweenthe first and second annular steps 22 and 26. Each of the recesses 28has a tapered lower end 30 and an upper end which opens into the firstannular step 22. The locking ring 24 has the same radial dimensions asthe first annular step 22 and, when secured in position, defines witheach recess 28 an upwardly facing shoulder 32. The shoulder 32 could beintegrally moulded with the barrel 12 but is formed by the separatelocking ring 24 for ease of manufacture. Opposed locating guides 34 forthe needle mount are moulded onto the inner surface of the one end 20 ofthe barrel between the first and second annular steps 22 and 26. Alocating projection (not shown) may be moulded into the otherwise smoothcylindrical barrel wall 36 above the first annular step 22 in order tohelp locate the locking ring 24 before it is secured in place, and anannular sealing ridge (not shown) may be integrally moulded into theinner surface of an outer end portion 38 of the one end 20 of the barrelbetween the second annular step 26 and an end face 40.

Referring now to FIGS. 1 to 7, the needle mount 16 has a main bodyportion 42, a skirt portion 44 and a needle seat 46. The needle mount 16is introduced to the barrel from the opposite end 48 (FIGS. 12 and 13)and has an annular shoulder 50 between the main body portion 42 and theskirt portion 44 which engages the second annular step 26 to prevent theneedle mount from being pulled outwardly through the open outer endportion 38 of the one end 20 of the barrel. With the needle mount seatedon the second annular step 26, the needle seat 46 projects from the oneend 20 of the barrel and defines a male lure tapered surface 52 ontowhich a needle assembly (not shown) may be seated. The needle assemblymay be as illustrated in our aforementioned earlier patent applicationand comprise a needle cannula or hypodermic needle fixed to a needle hubhaving a female lure tapered connector surface which cooperates with thelure surface 52 of the needle seat 46. This arrangement ensures thatdifferent sized needles can be used with the syringe 10 without havingto change the needle mount 16. The needle mount has an axial injectateflow passage 54 through the main portion 42 and needle seat 46.

As clearly shown in FIGS. 1 to 3, the needle seat 46 merges with themain body portion 42 and the skirt portion 44 extends around the upperpart of the needle seat, spaced therefrom by an annular groove 56 whichis deeper at two opposed portions 58. The skirt portion is a closesliding fit in and has substantially the same length as the outer endportion 38 of the one end 20 of the barrel, and its inherent resilienceassists the sealing of the needle mount in the barrel. In addition, thegroove 56/58 helps to reduce the volume of plastics material in theneedle mount. This helps to reduce shrinkage of the needle mount oncooling after injection moulding and thereby to maintain the circularcross-section of the needle mount.

The main body portion 42 of the needle mount 16 is sized to be closelyreceived in the one end 20 of the barrel between the first and secondannular steps 22 and 26. Opposed guide recesses 60 in the outer surfaceof the main body portion cooperate with the locating guides 34 in theone end 20 of the barrel to ensure a desired axial or rotationalorientation when the needle mount 16 is properly located in said oneend. The axial orientation of the needle mount is important in order toensure that projections 62 provided on radially outer surfaces ofopposed arms 64 of the needle mount cooperate with the recesses 28 inthe inner surface of the one end of the barrel, as shown in FIG. 1, tosecure the needle mount in the one end 20 of the barrel.

When the needle mount 16 is secured in the one end 20 of the barrel, theresiliently flexible arms 64 project into the barrel from said one endbeyond the main body portion 52 of the needle mount. The arms 64 arepivoted from adjacent the annular shoulder 50 in respective opposedaxially tapered grooves 66 formed in the side wall of the main bodyportion 42. The resilient flexibility of each arm is provided in themain by an integral joint 68 by which it is connected with the main bodyportion, but some resilient flexibility is also inherent in each armitself by virtue of its small dimensions, having a cross-section of, forexample, about 2 mm by about 2 mm. As clearly shown in FIGS. 4 and 7,the arms 64 are a close sliding fit in the grooves 66 so as to resistsideways deformation and twisting of the arms under load and to minimisethe volume of the dead space in the grooves.

As clearly shown in FIGS. 4 to 6, in their relaxed condition the arms 64project radially outwardly beyond the periphery of the main body portion42 of the needle mount so that when the needle mount is located in theone end 20 of the barrel the arms are biased radially outwardly toensure that the projection 62 on each arm engages the correspondingrecess 28 in the one end of the barrel. As the needle mount isintroduced to the one end of the barrel, this means that the projection62 rides over the locking ring 24 before snap engaging the respectiverecess, and to facilitate this the bottom edge 70 of each projection 62is inclined radially inwardly. The inclined bottom surface 30 of eachrecess 28 corresponds to the surface 70 and the projections 62 are aclose fit in the recesses 28, again so as to minimise the volume of thedead space in the one end of the barrel. The upper surface 72 of theprojection 62 on each arm extends normal to the length of the arm andtherefore substantially normal to the axis of the syringe to define ashoulder which cooperates with the shoulder 32 of each barrel recess 28to lock the needle mount against inadvertent withdrawal into the barrel,for example when a needle hub is being mounted on the needle seat 46 orwhen a needle of the syringe is being introduced to flesh during use.

The distal end 74 of each arm 64 projecting beyond an axially inner endface 76 of the main body portion 42 of the needle mount defines aninclined end face 78 and a radially outwardly projecting catch portion79 including a catch surface 80.

The axially inner end face 76 of the main body portion 42 of the needlemount is generally concave as shown in FIG. 3, with the flow passage 54opening at that end into the bottom of the concavity. However, the sidewalls 82 and inner wall 84 of the grooves 66 in which the arms 64 areresiliently displaceable extend to a substantially flat surface 86substantially at the peripheral height of the main body portion. Taperedside walls 88 and end wall 90 extend between the concave portion.

Referring to FIGS. 1, 2 and 8 to 11, the plunger 14 comprises a shaft 94with a head 96 at one end and a handle 98 at the other end. The shaft 94is of constant cruciform cross-section except where it tapers adjacentthe handle 98 and at a neck portion 100 adjacent the head 96. At theneck portion 100, the cross-section is reduced by a V-shaped notch ineach leg of the cruciform section to enable the shaft to be readilysnapped at that point when the plunger is withdrawn towards the otherend 48 of the syringe barrel.

The head 96 of the plunger carries the sealing ring 18 which acts as apiston to eject injectate in the syringe through the flow passage 54.The sealing ring 18 bears against an annular flange 102 which is ofslightly smaller radius than the internal radius of the barrel, and hasan annular portion 104 which is seated in an annular recess 106 in thehead. The annular end flange 108 of the head of the plunger is taperedto facilitate location of the sealing ring on the head.

The end face 110 of the plunger head 96 is generally convex andcorresponds substantially in shape to the axially inner end face 76 ofthe needle mount 16. Thus, the convexity of the end face is broken byopposed recesses 112 which correspond in shape to and closely receiverespective projecting wall and surface portions 82, 84, 86, 88 and 90 onthe needle mount end face 76.

Projecting generally axially inwardly from each recess 112 is arespective slot 114 in the end face 110 of the plunger head which issized to closely receive the distal end 74 of the respective arm 64 ofthe needle mount. In particular, the width of each slot 114 is such asto closely receive the distal end of the respective arm 64 so as toresist any sideways deformation or twisting of the arm and the depth andradial length of each slot 114 is essentially such as to permit thedesired radial movement of the arm described hereinafter. In addition toresisting deformation and twisting of the arm, the describeddimensioning of each slot 114 reduces the volume of the dead spacebetween the engaged plunger and needle mount.

The radially outer side of each slot 114 is inclined radially outwardlytowards the plunger end face 110 in two stages 116 and 118 interruptedby a recess 120. The first inclined face 116 in each slot 114 defines aramp surface which is adapted to cooperate with the inclined face 78 onthe distal end 74 of the respective arm 64 as the plunger 14 is movedtowards the needle mount to pivot the arm 64 radially inwardly againstits inherent bias and thereby disengage the arm projection 62 from thebarrel recess 28. With further movement of the plunger towards theneedle mount, the radially outermost catch portion 79 of the distal end74 of the arm, including the catch surface 80, rides over the inclinedface 116 and aligns with the respective recess 120 in the slot 114, atwhich stage the radially outwards bias of the arm causes the catchportion 79 to snap into the recess 120. The second inclined face 118 ofthe slot 114 is displaced sufficiently from the line of the firstinclined face 116 to enable this to occur, and is then in at least nearcontact with the inclined face 78 of the distal end of the arm 64 so asto reduce the volume of the dead space between the engaged plunger andneedle mount. In this condition, the bias of the arm 64 allows the catchsurface 80 on the arm 64 to cooperate with an engagement surface 122 ofthe respective recess, as seen in FIG. 2, to enable the plunger towithdraw the needle mount and any attached needle assembly into thebarrel as the plunger is withdrawn towards the opposite end 48 of thebarrel. Once the projections 62 on the arms 64 have been released fromthe barrel recesses 28, the needle mount is substantially freelywithdrawable into the barrel.

For ease of manufacture, the recesses 120 open radially outwardly intothe annular recess 106 in the plunger head but are sealed by the sealingring 18 and define negligible dead space. When the needle mount isengaged by the plunger head, the end face 110 of the plunger head is innear contact to the correspondingly shaped inner end face 92 of theneedle mount but does not seal the injectate flow path 54 through theneedle mount since any premature sealing will prevent injectate frombeing expelled and increase the volume of retained injectate. In theillustrated embodiment the dead space between the engaged needle mountand plunger can readily be within the 0.075 ml tolerance.

Since the distal ends 74 of the arms 64 of the needle mount are closelyreceived in the slots 114 in the plunger head, it is important to ensurethat the plunger is correctly aligned rotationally with the needlemount. This is achieved by cruciform guide slots 124 which are definedby integrally hinged end members 126 at the other end 48 of the syringebarrel 12. Prior to assembly of the syringe, the end members 126 are intheir open condition as shown in FIGS. 12 to 14. The recesses 28 andlocating guides 34 have been omitted from FIG. 14 for convenience only.When the plunger has been introduced into the barrel, the end members126 may be folded over the end of the barrel about the respectiveintegral hinges 128. The slots 124 in the end members 126 define acruciform cross-section which closely corresponds to that of the plungershaft 94 so that the end members may be folded into position around therotationally aligned shaft. Rotation alignment of the various parts ofthe syringe is ensured by the appropriate rotational location of thelocating guides 34 and the recesses 28 in the one end 20 of the barrelwith the end member slots 124, the appropriate rotational location ofthe arms 64 with the cooperating locating guides 60 on the needle mountand the appropriate rotational location of the slots 114 in the plungerhead with the shaft cruciform section. As the end members 126 are foldedover, respective cylindrical locating plugs 130 are received incorresponding openings 132 on an end flange 134 to which the end membersare hinged Similarly, a tapered semi-circular wall member 136 extendingaround the slots 124 on each end member, having a diameter correspondingto the cruciform cross-section, is received in the tapered opening 138at the other end of the barrel. Once the end members are fully locatedin the closed condition shown in FIGS. 15 and 16, they may be secured inthat condition by, for example, ultrasonically welding the end membersto the flange 134 to prevent the plunger head 96 being withdrawn, withor without the needle mount 16 engaged therewith, past the end members.

Means are also provided to prevent the fully withdrawn plunger beingdisplaced again towards the one end 20 of the barrel. Such meanscomprise opposed integral tabs 140 moulded onto the cruciformcross-section of the plunger shaft 94 adjacent the necked portion 100thereof. The tabs 140 have an inclined upper face 142 which facilitatestheir displacement through the cruciform slots 124 in the secured endmembers 126, by either or both of the relatively thin portions 143 ofthe end members 126 defining the slots 124 and the tabs 140 resilientlydeforming. The tabs 140 also have a lower face 144 which extends normalto the axis of the plunger shaft 94 and which, by engagement with theupper surface 146 of the portions 143 of the end members 126 adjacentthe slots 124, resist passage back through the slots 124 and thereforereintroduction of the plunger into the barrel. In addition to thismeasure, the plunger shaft may be snapped through the necked portion100, as previously described, immediately adjacent the tabs 140. Thereis then no means to facilitate the reintroduction of the plunger to thebarrel. This is illustrated in FIG. 16.

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionincludes all such variations and modifications which fall within the itsspirit and scope. The invention also includes all of the steps andfeatures referred to or indicated in this specification, individually orcollectively, and any and all combinations of any two or more of saidsteps or features. In particular, it will be appreciated that many ofthe features of the syringe described herein may be used independentlyof other features, and any such feature should accordingly be consideredas an independent invention which may be defined separately from otherfeatures in this patent application.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word "comprise", or variations such as"comprises" or "comprising", will be understood to imply the inclusionof a stated integer or group of integers but not the exclusion of anyother integer or group of integers.

We claim:
 1. A syringe comprising a barrel having an openingtherethrough at one end, a plunger operable along a longitudinal axis ofthe barrel within the barrel and a needle mount in the opening, saidneedle mount having an axially inner end and being prevented fromdisplacement outwardly through the opening, said needle mount furtherhaving a securing portion comprising a resiliently flexible armextending generally away from said one end of the barrel, towards theplunger, said arm having a shoulder on a radially outwards surfacethereof which cooperates with a shoulder on the barrel wall to resistwithdrawal of the needle mount from the opening into the barrel, thesyringe further comprising a surface portion on the plunger to deformthe arm radially inwardly as the plunger approaches the axially innerend of the needle mount thereby to disengage the arm from the barrelwall shoulder, and cooperable engagement surfaces on the plunger and ona distal end of the arm whereby the plunger is capable of engaging thedisengaged needle mount for withdrawal of the needle mount into thebarrel when the plunger is displaced away from said one end of thebarrel, wherein the arm is received in a slot when the arm is engaged bythe plunger for withdrawal of the needle mount into the barrel, saidslot being provided to resist sideways deformation of the arm by havingsuch a width as to closely receive the arm, and said arm being radiallydisplaceable in the slot.
 2. A syringe according to claim 1, wherein thearm projects into the barrel relative to at least adjacent portions ofthe needle mount and the slot is in an end face of the plunger whichreceives the distal end of the arm.
 3. A syringe according to claim 2wherein the engagement surface on the plunger is provided in the slot.4. A syringe according to claim 2 wherein the deforming surface portionon the plunger is provided in the slot.
 5. A syringe according to claim1 wherein the deforming surface portion on the plunger engages a rampsurface on the arm.
 6. A syringe according to claim 1 wherein theresiliently flexible arm of the needle mount is pivoted from the side ofthe needle mount at a location remote from the axially inner end of theneedle mount.
 7. A syringe according to claim 6, wherein the needlemount has a side wall and the arm is deformable radially inwardly in aslot in the side wall of the needle mount, said slot having such a widthas to closely receive the arm therein.
 8. A syringe according to claim 1wherein the resiliently flexible arm is pivoted relative to a body ofthe needle mount about an integral joint which provides at least themajority of the resilient flexibility of the arm.
 9. A syringe accordingto claim 1 wherein the resilient flexibility of the arm biases the armto normally maintain the cooperation between the respective shoulders onthe arm and on the barrel wall and, during withdrawal of the needlemount, between the cooperable surfaces on the plunger and on the distalend of the arm.
 10. A syringe according to claim 1 wherein the shoulderon the resiliently flexible arm of the needle mount is closely receivedin an associated recess including the barrel wall shoulder whichsubstantially conforms to a portion of the arm on which the arm shoulderis formed.
 11. A syringe according to claim 1 wherein the needle mountsecuring portion comprises a second resiliently flexible arm extendinggenerally away from said one end towards the plunger, said second armhaving a shoulder on a radially outwards surface thereof whichcooperates with a respective shoulder on the barrel wall to resistwithdrawal of the needle mount from the opening into the barrel, asecond surface portion being provided on the plunger to deform thesecond arm radially inwardly as the plunger approaches the needle mountto disengage the second arm from the associated barrel wall shoulder.12. A syringe according to claim 11 wherein cooperable engagementsurfaces are provided on the plunger and engagement surfaces areprovided on the plunger and on the distal end of the second arm wherebythe plunger is capable of engaging the disengaged needle mount therebyto facilitate withdrawal of the needle mount into the barrel when theplunger is displaced away from said one end of the barrel, and means isprovided to resist sideways deformation of the second arm when the armis engaged by the plunger for withdrawal of the needle into the barrel.13. A syringe according to claim 12 wherein the means to resist sidewaysdeformation of the second arm comprises associated slot means in whichthe second arm is radially displaceable, the slot means having such awidth as to closely receive the second arm.
 14. A syringe according toclaim 13 wherein the second arm projects into the barrel relative to atleast adjacent portions of the needle mount and the associated slotmeans comprises a respective slot in the end face of the plunger whichreceives the distal end of the second arm.
 15. A syringe according toclaim 14 wherein the associated engagement surface on the plunger isprovided in the slot for the second arm.
 16. A syringe according toclaim 14 wherein the deforming portion on the plunger for the second armis provided in the respective slot.
 17. A syringe according to claim 12wherein the means to resist sideways deformation of the second armcorresponds to the means to resist sideways deformation of thefirst-mentioned arm.
 18. A syringe according to claim 11 wherein thedeforming surface portion on the plunger for the second arm engages aramp surface on the second arm.
 19. A syringe according to claim 11wherein the resiliently flexible second arm is pivoted from the side ofthe needle mount at a location remote from the axially inner end of theneedle mount.
 20. A syringe according to claim 19 wherein the needlemount has a side wall and the second arm is deformable radially inwardlyin a respective slot in the side wall of the needle mount, said slothaving such a width as to closely receive the second arm therein.
 21. Asyringe according to claim 11 wherein the resiliently flexible secondarm is pivoted relative to a body of the needle mount about an integraljoint which provides at least the majority of the resilient flexibilityof the second arm.
 22. A syringe according to claim 11 wherein theresilient flexibility of the second arm biases the arm to normallymaintain the cooperation between the respective shoulders on the secondarm and on the barrel wall.
 23. A syringe according to claim 11 whereinthe shoulder on the resiliently flexible second arm is closely receivedin an associated recess including the respective barrel wall shoulderwhich substantially conforms to a portion of the second arm on which thearm shoulder is formed.
 24. A syringe according to claim 1 wherein anend face of the plunger has a substantial part of its surface area in atleast very close overlying relationship with a corresponding end face ofthe needle mount when the plunger and needle mount are engaged.
 25. Asyringe according to claim 1 wherein the needle mount has an injectateflow passage therethrough for directing the injectate to a cannula orneedle in use, and the flow passage is not sealed by the plunger whenthe plunger cooperably engages the needle mount.
 26. A syringe accordingto claim 1, wherein cooperable locating means are provided on the needlemount and on the barrel wall to rotationally orientate the needle mountrelative to the barrel about the longitudinal axis of the barrel.
 27. Asyringe according to claim 1, wherein axial guide means is provided torotationally orientate the plunger relative to the barrel about thelongitudinal axis of the barrel.
 28. A syringe according to claim 27,wherein the plunger has a shaft which projects from an opening at theother end of the barrel, the plunger shaft having a non-circularcross-section, and the axial guide means is integrally moulded with thebarrel and is connected thereto by integral hinge means whereby in anopen condition of the guide means a plunger piston may be introduced tothe barrel through said opening and in the closed condition the axialguide means overlies the other end of the barrel and partly closes saidopening to cooperate with said non-circular cross-section of the shaftto provide said rotational orientation.
 29. A syringe according to claim28 wherein the axial guide means comprises locating means whichcooperates with corresponding means on an end face of the barrel at theother end when the guide means is in its closed condition.
 30. A syringeaccording to claim 28 wherein the axial guide means comprises opposedguide members each of which is integrally hinged to the barrel at theother end, on opposite sides of the opening.
 31. A syringe according toclaim 30 wherein when the guide members are folded into the closedcondition they together define an aperture therethrough whichsubstantially corresponds in cross-section to that of the plunger shaft.32. A syringe according to claim 28 wherein cooperating means areprovided on the plunger and on the barrel to prevent forward movement ofthe plunger once the plunger has been withdrawn into the barrel after aninjecting stroke, the cooperating means comprising a catch on theplunger which cooperates with the axial guide means.
 33. A syringeaccording to claim 1 wherein cooperating means are provided on theplunger and on the barrel to prevent forward movement of the plungeronce the plunger has been withdrawn into the barrel after an injectingstroke.
 34. A syringe according to claim 1 wherein the plunger has aline of weakness adjacent a piston thereof which is exposed when theplunger has been withdrawn after an injecting stroke.
 35. A syringeaccording to claim 1 wherein the barrel is moulded and the shoulder onthe barrel wall is defined by an insert secured to the barrel.
 36. Asyringe according to claim 35 wherein the insert comprises a ring.
 37. Asyringe according to claim 35 wherein the insert is located by a step inthe barrel wall.
 38. A syringe according to claim 37 wherein the stepextends fully around the barrel wall and has a radial width no greaterthan the insert except where the shoulder is defined.
 39. A syringeaccording to claim 37 wherein two opposed recesses are formed in thestep to define with the insert respective opposed shoulders on thebarrel wall.
 40. A syringe according to claim 1 wherein the opening insaid one end of the barrel has a smaller cross-section than the internalcross-section of the remainder of the barrel.